Oil fields are typically found in remote locations. Crude oil is a mixture of hydrocarbonaceous compounds when it comes out of the ground. Typical maximum temperatures for conventional crude carriers are 140° F. (60° C.). Waxy crude oils must be shipped in specially equipped crude carriers at temperatures up to around 160° F. (71° C.). Slack waxes from petroleum deoiling and dewaxing operations must also be shipped in a molten state at elevated temperatures in specialty chemical tankers. Waxy crude oils and slack waxes that can be shipped in these specially equipped carriers or specialty tankers are typically required to have pour points at least 110° F. below the shipping temperature. Shipping crude oils and waxes with pour points at least 10° F. below the temperature of shipping in the specially equipped carrier or specialty tanker provides a measure of protection against an excessive amount of solid wax forming during the voyage. While some solid wax can be tolerated during unloading, formation of an excessive amount of solid wax requires a lengthy and costly operation to melt the solid wax. The use of conventional crude carriers, those that ship materials at temperatures at or below 140° F., is preferred whenever possible because these carriers have a significantly lower cost of transport.
Similarly, when crude oil is shipped in a pipeline, materials that are pumpable at near ambient conditions are preferred because these materials avoid the need for heated pipelines. Similar shipping considerations exist for transporting waxy crude oil in railcars and trucks. Materials that are pumpable at or near ambient conditions are preferred due to the significantly lower cost of transport.
Like crude oil, natural gas and coal assets are often located at remote sites. It is often more commercially feasible to convert these resources into synthesis gas and then into higher molecular weight hydrocarbons at the remote sites rather than attempting to transport the natural gas and coal assets to another location for conversion. Many processes, including Fischer-Tropsch synthesis, can be used to convert synthesis gas from methane or coal to higher molecular weight hydrocarbons. The products of Fischer-Tropsch synthesis are mostly linear hydrocarbons, these products often include a high melting point paraffinic wax. From the Fischer-Tropsch products, a C5+ containing product stream, which is solid at room temperature, can be isolated. This product stream is commonly referred to as “syncrude.”
When capital costs at the remote sites, where the natural gas and coal assets are located, are high, it is desirable to limit the amount of processing equipment at the remote locations. Accordingly, it is desirable to transport the syncrude to existing commercial refineries for upgrading to provide finished, salable products.
Since it is desirable to transport waxy petroleum crude and Fischer-Tropsch products, including Fischer-Tropsch syncrude, from remote sites to distant commercial refineries, there have been attempts to develop acceptable approaches for this transportation.
U.S. Pat. Nos. 5,968,991; 5,945,459; 5,863,856; 5,856,261; and 5,856,260 disclose a catalyst useful in Fischer-Tropsch reactions and products produced by these reactions. These patents further disclose that a liquid product of a Fischer-Tropsch reactor can be produced and shipped from a remote area to a refinery site for further chemical reacting and upgrading to a variety of products, or produced and upgraded at a refinery site.
There have been several approaches developed to transport the waxy Fischer-Tropsch product. One approach to shipping waxy Fischer-Tropsch products, as disclosed in U.S. Pat. No. 5,866,751, is to isolate C20-36 waxy hydrocarbons from the Fischer-Tropsch products. U.S. Pat. No. 5,866,751 discloses transporting long-chain, non-volatile, solid paraffin wax hydrocarbons in the C20-36 range in solid form from a remote site to a local site. However, transporting solids requires expensive forming, loading, and unloading facilities and thus, is difficult and expensive.
Another approach has focused on transporting a Fischer-Tropsch syncrude that has been partially upgraded to convert some of the linear hydrocarbons into iso-paraffins, as disclosed in U.S. Pat. No. 5,292,989. U.S. Pat. No. 5,292,989 discloses that to achieve a pumpable product, the Fischer-Tropsch wax is isomerized to convert some of the normal paraffins to branched paraffins. Isomerization provides a syncrude that is near liquid at ambient temperature, and therefore, is more easily transportable. However, this upgrading may require the construction of facilities, which are expensive and difficult to operate in remote locations.
U.S. Pat. Nos. 6,313,361 and 6,294,076 disclose transporting a mixture of Fischer-Tropsch wax in lighter hydrocarbon liquid. In U.S. Pat. No. 6,294,076, the Fischer-Tropsch wax is granulated into finely divided flakes and then mixed with naphtha in a colloid mill. As disclosed, to provide a pumpable mixture at ambient temperature, the mixture can contain from about 1 to 22 weight % Fischer-Tropsch wax, preferably from about 8 to 10 weight % Fischer-Tropsch wax. However, since the ratio of wax to light hydrocarbons produced from a Fischer-Tropsch process is greater than 25 weight %, this approach cannot transport all of the Fischer-Tropsch wax from the remote location. In U.S. Pat. No. 6,313,361, a slurry is formed from unconsolidated solid wax particles and lighter liquid paraffinic compounds. As disclosed, to provide a stable slurry, the solid wax particles make up about 5 to 30% by volume of the slurry.
Accordingly, efficient methods of transporting waxy hydrocarbons in a pumpable form are desired. It is desired that these methods provide for transportation of the waxy hydrocarbons in a pumpable form without requiring expensive upgrading facilities, without corrosion to the transportation equipment, without requiring the use of heated transportation equipment, and with a safe vapor pressure. Moreover, it is desired that these methods allow for transportation of a product that contains greater than 30 weight % waxy hydrocarbons.